Modern wireless telecommunications systems are evolving to provide high speed packet data services for users of mobile equipment. One example is an ability to provide internet access to a user of mobile equipment. A wireless system that is rapidly evolving in this direction is a Time Division, Multiple Access (TDMA) system known as the Global System for Mobile Communication (GSM), in particular enhanced versions of GSM known as GSM+, GPRS (General Packet Radio Services) and EGPRS (Enhanced General Packet Radio Services).
In EGPRS the same access types as in GPRS are supported to establish a so-called temporary block flow (TBF) in the uplink direction (i.e., from the mobile equipment to the network). To accomplish this, a control message used by a GPRS mobile equipment to request a packet channel (Packet Channel Request, 11 bits) is re-used for EGPRS. FIG. 1 illustrates the format of the conventional GPRS 11-bit Packet Channel Request message.
The Packet Channel Request message indicates what type of access the mobile station requires. The different access types that can be used when establishing an EGPRS connection are as follows.
(A) One Phase Access Request (OPAR)
OPAR is the fasted and most effective way of TBF establishment. However, setting up a TBF in EGPRS mode does not automatically imply that the mobile equipment use coherent 8-PSK modulation on the uplink. In fact, the network can order the mobile equipment to use any type of modulation, including Gaussian Mean Shift Keying (GMSK) based modulation schemes.
(B) Short Access Request (SAR)
SAR is employed when a small number of Radio Link Control (RLC) blocks (<=8) need to be transmitted. It is possible to include an EGPRS SAR, however the gain is considered to be low when compared to the standard GPRS SAR.
(C) Two Phase Access Request (TPAR)
TPAR requires more signalling than OPAR and SAR before the TBF is actually set up.
The 11 bits of the Packet Channel Request message permit the indication of 2048 different bit patterns, among which GPRS already uses 1024 for OPAR, 256 for SAR and a total of 160 for the others (TPAR, as well as page response, cell update, mobility management procedure and single block without TBF establishment). This results in only 608 available bit pattern combinations for EGPRS and future enhancements, which is clearly not sufficient.
For EGPRS it has been proposed that the 11-bit Packet Channel Request Message be modified to accommodate the uplink modulation and multislot requirements (ETSI SMG2 Working Session on Edge, Tdoc SMG2 EDGE 134/99, “Uplink TBF Establishment for EGPRS”, Ericsson, May 17th-9th, 1999, Bois d'Arcy, France.
This approach is generally not adequate, as it requires that further changes and assumptions be made to and in the packet radio service signalling protocols.